Internal combustion engines utilize multiple combustion spaces defined within the cylinders of the engine to contain and direct the forces resulting from the combustion of fuel therein. These combustion spaces are typically irregularly shaped and vary in volume depending on the location of the piston within the cylinder. For an efficient and balanced engine, the combustion spaces in all engine cylinders must be calibrated to produce identical volumes at the time of fuel detonation. Such a balanced engine produces an even distribution of power to the crank shaft and consistent fuel consumption among the engine cylinders.
Helmholtz acoustic resonators have been utilized to determine the volume of an unknown test cavity. A Helmholtz acoustic resonator utilizes low frequency resonating waves to produce acoustical vibrations from within various cavities. The acoustical vibrations depend solely on the volume of cavity independent of its geometry. Resonating waves are directed into the unknown test cavity, producing an acoustical vibration corresponding to the unknown volume of the test cavity. Additionally, resonating waves are directed into a standard volume cavity, producing a standard acoustical vibration corresponding to a known volume. Sensors are positioned to detect these discrete acoustical vibrations. If the vibrations are identical in amplitude and frequency, the volumes are also identical. If the vibrations are different, the difference between the frequencies corresponds to the differences between the volumes. Examples of such acoustical-measuring apparatus include Poole et al., U.S. Pat. No. 2,666,326 and Mathias, U.S. Pat. No. 3,075,382.
The principle of the Helmholtz resonator is based on the fact that the resonance frequency generated by an acoustic resonator having an access passage is dependent on the volume of the resonator cavity and the dimensions of the access passageway. If the access passageway has a small volume relative to the resonator cavity, the resonance frequency is based on the volume of the resonator cavity alone. The resonance frequency is determined independent of the geometry or shape of the resonator cavity. Therefore, the volume of the cavity is solely as function of the resonance frequency of the cavity.
The prior art utilizes this principle by comparing a resonant frequency signal generated from within an unknown volume cavity to a resonant frequency signal generated from within a known (or standard) volume cavity. The difference in these frequencies is a measure of the volume of the unknown cavity compared to the volume of the standard cavity. More precisely, the volume of the unknown cavity is a function of the difference between the generated frequencies.
Typically, these devices utilize a single resonator associated with the unknown volume cavity which was compared to an absolute value produced from the known volume standard cavity. This allows for external factors to influence the accuracy of the measuring device. When these devices utilize multiple resonators, such as is disclosed in U.S. Pat. No. 2,666,326, the effect of external factors are minimized. The standard volume cavities being positioned in close proximity to the unknown cavity so as to be equally affected by changes in pressure, temperature and/or humidity.
The prior art, however requires complex mathematical processing to determine the exact volume of an unknown cavity from the resonant frequency of a standard volume. The present invention offers a greatly simplified substitute for the current volumetric measuring devices and methodology.